
// 如果能拆成字符串，就返回第一个字母，否则返回 never
type FirstChar<T> = T extends `${infer L}${infer R}` ? L : never



type A = FirstChar<'BFE'> // 'B'
type B = FirstChar<'dev'> // 'd'
type C = FirstChar<''> // never


export {}